Small holes drilled into a workpiece can be machined to form a precision finished surface on the hole walls, by rotating the workpiece on a lathe while a cutting insert is advanced within the hole. The cutting insert is mounted in a pocket of a holder head. It is often desirable to detachably mount the holder head on a holder bar device so the head can be replaced. In prior systems, holder heads on bar devices of ⅝th inch and larger diameters are held by a multiple screw/multiple serration system. In that system, precision mounting of the head on the bar device is achieved by miniature screws and multiple serrations on each part that interfit. For bar diameters of under ⅝th inch the cost to manufacture a screw and serration configuration makes such system impractical. In prior art systems for bar diameters under ⅝th inch the holder device is simply brazed to the bar device in a one piece construction.
It would be desirable if a machining apparatus were available that could be practically built on smaller shanks such as those of ⅜ths inch diameter, and that was of simpler and lower cost construction. If the holder head could be easily replaced on the bar device, a holder head could be used that had an insert-holding pocket that could receive a particular type of cutting insert, and a damaged head could be replaced on a holder device without removal from the machine tool.